Soft capsules are differently sized and differently shaped capsules formed by pressing and encapsulating oily functional substances, functional substance solutions or functional substance powder within gelatin membranes in controlled quantities. Soft capsules are a traditional formulation that finds wide applications in such fields as medicines, cosmetics and colored ball fabrication. Soft capsule products put a very high demand on the precision of loading amount.
Currently commercially available rotary die soft capsule producing devices generally make use of plunger pumps to fill in the contents of the soft capsules. Filling by plunger pumps has the advantages of highly consistent pill shapes, few difference in loading amounts, and compactness in structures, etc. To complete filling in a soft capsule, it is required that the plunger pump be able to continuously perform the actions of liquid suction and liquid injection, and that there must be means for switching between the liquid suction passage and the liquid injection passage. When the switching means opens the liquid suction hole, the liquid suction passage is communicative, and the plunger movement completes the liquid suction action. When the switching means opens the liquid injection hole, the liquid injection passage is communicative, and the plunger movement completes the liquid injection action.
The main structure of the means, or in other words the plunger pump, of a current rotary die soft capsule producing device for achieving the aforementioned functional requirements is as follows: a switchover plate is used to switch between opening and closing of the liquid suction hole and the liquid injection hole; it is usual to provide the switchover plate with multiple rows of channels (the number of channel rows can be different with the differing type models and yields of the soft capsule producing devices); the switchover plate moves to enable the corresponding channel to be communicative with the liquid suction passage or the liquid injection passage; the switchover plate cooperates and is assembled together with guide track pieces and upper and lower plates at both sides thereof in fixed gaps. Moreover, the switchover plate normally operates only when it has been lubricated by lubricating oil. The structure has the following main defects.
1) Since the communicative passage of the medical solution is opened or closed incessantly by means of the linearly reciprocating movement of the switchover plate, it is inevitable for the somewhat pressurized medical solution to “run” out from lateral gaps of the switchover plate, thereby affecting the precision in the loading amount of the soft capsule.
2) Since the lubricating oil has certain pressure, it infiltrates in the medical solution via lateral gaps of the switchover plate, thereby affecting the components and quality of the medical solution of the soft capsule.
3) The switchover plate is always in a state of violent attrition during the process of fabricating the soft capsule, and such attrition enlarges the gaps of the switchover plate in circumferential direction, so that this necessitates periodic maintenance of the plunger pump to adjust the gaps to proper size.
4) Suspension liquid having fine particulates is unsuited to serve as mother liquid, as the fine particulates would aggravate wearing-out of the switchover plate, thereby affecting the performance and use life of the plunger pump.